LARIN 1/20
Clinical safety rating
cautionComprehensive clinical and safety monograph for LARIN 1/20 (LARIN 1/20).
Combination estrogen-progestin contraceptive; suppresses gonadotropins (FSH, LH) via negative feedback on hypothalamic-pituitary axis, inhibiting ovulation; increases cervical mucus viscosity, inhibiting sperm penetration; alters endometrial receptivity.
| Metabolism | Ethinyl estradiol: primarily metabolized by CYP3A4; undergoes first-pass metabolism in gut and liver. Norethindrone: primarily metabolized by reduction and conjugation; substrate of CYP3A4. |
| Excretion | Approximately 60% renal (30% norethindrone, 30% ethinyl estradiol metabolites) and 40% fecal (biliary excretion of conjugates). |
| Half-life | Norethindrone: 7.6 hours (range 5-14); Ethinyl estradiol: 13.2 hours (range 8-20). Clinical context: Steady-state achieved within 5-10 days. |
| Protein binding | Norethindrone: 61% (albumin, SHBG); Ethinyl estradiol: 97% (albumin). |
| Volume of Distribution | Norethindrone: 3.8 L/kg; Ethinyl estradiol: 2.8 L/kg. Indicates extensive tissue distribution. |
| Bioavailability | Oral: Norethindrone 64% (first-pass metabolism); Ethinyl estradiol 38-48% (first-pass metabolism). |
| Onset of Action | Oral: 1-3 days for contraceptive effect (ovulation suppression requires ≥7 days of consistent use). |
| Duration of Action | 24 hours (daily dosing required). Clinical note: Missed dose reduces efficacy; back-up contraception needed if >36-hour interval. |
| Molecular Weight | 361.5 |
| Action Class | Combination Oral Contraceptive (Estrogen-Progestin) |
One tablet (0.1 mg levonorgestrel/20 mcg ethinyl estradiol) orally once daily for 21 days followed by 7 placebo days.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment. Contraindicated in severe renal impairment (GFR <30 mL/min) due to potential fluid retention and metabolic acidosis. |
| Liver impairment | Contraindicated in acute hepatic disease, hepatic adenomas, or severe cirrhosis (Child-Pugh class C). No specific dose adjustments provided for mild to moderate impairment; use caution. |
| Pediatric use | Not indicated for use before menarche. For postmenarchal adolescents, same dosing as adults: one tablet orally once daily for 21 days followed by 7 placebo days. |
| Geriatric use | Not indicated for use after menopause. No specific dose adjustments in elderly; increased risk of thrombosis and hypoglycemia warrants caution. |
| 1st trimester | Contraindicated in pregnancy. Use during first trimester is associated with an increased risk of congenital anomalies, particularly cardiovascular and limb defects. Pregnancy should be excluded before initiation. |
| 2nd trimester | Contraindicated. Use during second trimester may be associated with adverse fetal outcomes, including potential effects on fetal development. Data limited but risk is considered significant. |
| 3rd trimester | Contraindicated. Use during third trimester may cause fetal harm, including potential effects on fetal genital development in males (if androgenic progestin component). Avoid in pregnant women. |
Clinical note
Comprehensive clinical and safety monograph for LARIN 1/20 (LARIN 1/20).
| Placental transfer | Both ethinyl estradiol and norethindrone cross the placenta. Drug concentrations in fetal circulation approximate maternal levels. Placental transfer has been documented in animal and human studies. |
| Breastfeeding | Small amounts of ethinyl estradiol and norethindrone (the components of Larin 1/20) are excreted in breast milk. Use during breastfeeding may reduce milk production and affect infant development. Consider alternative contraception methods. Generally not recommended during breastfeeding, especially in the early postpartum period. |
| Lactation Rating | L4 (Possibly Hazardous) |
| Teratogenic Risk | LARIN 1/20 (norethindrone acetate/ethinyl estradiol) is contraindicated in pregnancy. First trimester: No increased risk of major birth defects from low-dose OCs in cohort studies, but an increased risk of cardiovascular malformations (e.g., VSD, TGA) and neural tube defects has been suggested in some studies; risk of oral cleft is not increased. Second/third trimesters: Use may increase risk of fetal hepatic adenoma, fetal feminization with androgenic progestins (norethindrone has minimal androgenicity), and potential for neonatal withdrawal bleeding or hormonal effects; no clear risk of pregnancy loss beyond baseline. |
| Fetal Monitoring | Pregnancy test before initiation if pregnancy suspected. No routine fetal monitoring required if used inadvertently; if exposure occurs in first trimester, offer prenatal diagnostic testing (ultrasound at 18-20 weeks for structural anomalies; consider fetal echocardiography if concerns). Monitor maternal blood pressure and liver function if prolonged use during pregnancy (rare). |
| Fertility Effects | LARIN 1/20 suppresses ovulation via inhibition of gonadotropins; normal fertility returns within 1-3 months after discontinuation. No permanent impairment of fertility. Post-pill amenorrhea may occur in <1% of users, usually resolving spontaneously; evaluate if >6 months. No adverse effects on oocyte quality or long-term reproductive capacity. |
■ FDA Black Box Warning
Cigarette smoking increases risk of serious cardiovascular events from combination oral contraceptives. Risk increases with age (especially >35 years) and with heavy smoking (≥15 cigarettes/day). Women who use combination hormonal contraceptives should not smoke.
| Common Effects | Nausea, Headache, Breast tenderness, Weight changes, Irregular menstrual bleeding (spotting, breakthrough bleeding), Mood changes (depression, anxiety), Acne (may improve or worsen), Decreased libido |
| Serious Effects | Venous thromboembolism (deep vein thrombosis, pulmonary embolism), Arterial thromboembolism (myocardial infarction, stroke), Hepatic adenoma or hepatocellular carcinoma, Hypertension, Gallbladder disease, Thrombotic thrombocytopenic purpura (TTP) in patients with factor V Leiden or other thrombophilias |
Known or suspected pregnancyBreast cancer (current or history)Undiagnosed abnormal uterine bleedingCurrent or history of venous thromboembolismActive liver disease or impaired liver functionCigarette smoking in women over 35 years of ageUncontrolled hypertensionDiabetes with vascular involvementMigraine with focal neurological symptoms (in women over 35)
| Precautions | Thrombotic disorders: discontinue if thrombophlebitis, thromboembolic, or vascular events occur, Carcinoma risk: increased risk of breast cancer; cervical cancer association, Hepatic effects: acute liver disease, liver tumors, Elevated blood pressure, Gallbladder disease, Carbohydrate/lipid metabolic effects, Ocular lesions: retinal thrombosis; discontinue if unexplained vision loss, Hereditary angioedema exacerbation, Chloasma, Pregnancy: discontinue if pregnancy occurs |
| Food/Dietary | Grapefruit and grapefruit juice may increase estrogen levels; limit intake. No other significant food interactions. Avoid St. John's wort (herbal supplement) as it reduces contraceptive efficacy. Alcohol may increase risk of liver toxicity; moderate consumption is generally acceptable. |
| Clinical Pearls | LARIN 1/20 (norethindrone acetate 1 mg/ethinyl estradiol 20 mcg) has a low estrogen dose, which may reduce estrogen-related side effects but can increase breakthrough bleeding. It is a monophasic pill. Starting on the first day of menses provides immediate contraceptive protection. Caution in patients with migraine with aura or uncontrolled hypertension. Check for drug interactions with CYP3A4 inducers (e.g., rifampin, St. John's wort). |
| Patient Advice | Take one pill daily at the same time; missing pills increases pregnancy risk. · If you miss a pill, follow the package instructions; use backup contraception if needed. · Common side effects include nausea, breast tenderness, and breakthrough bleeding, especially in the first few months. · Do not smoke while taking this medication, especially if over 35; smoking increases risk of serious cardiovascular events. · This pill does not protect against STIs; use condoms for protection. · Inform your healthcare provider of all medications and supplements you take, especially St. John's wort, antibiotics, and anticonvulsants. · Contact your doctor if you experience severe headache, chest pain, leg pain or swelling, sudden shortness of breath, or vision changes. |
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